At the present, there are active endeavors for developing a light emitting diode (LED) with high photoconversion efficiency by improving a nitride-based semiconductor growth structure or a grown film manufacturing process by using a nitride-based semiconductor with a great band gap. However, an LED TV known in the art until now adopts a white or three-color LED element as a backlight instead of a cold cathode fluorescent lamp (CCFL) backlight used in an existing LCD TV, and this is actually an LCD TV using an LED backlight. In detail, an outdoor electronic display board having several ten thousands or several hundred thousands of three-color (red, green and blue) LED lamps inserted into an ultra-large substrate is known as a full-color LED display available at the present, which is substantially a unique available product encountered everyday life. Therefore, in an accurate conception, an LED full-color display is not yet implemented at the present as a home TV or a computer monitor.
A display having a size of a TV or monitor has not been developed using an existing LED element due to the limits in a display manufacturing technique using an LED element and a full-color implementation technique. In an existing LED element manufacturing method, a p-semiconductor layer, a quantum well layer and a n-semiconductor layer of III-V group material are deposited to a sapphire substrate of 2 to 8 inches by means of metal organic chemical vapor deposition (MOCVD), and then an LED element of a desired shape is made through various post-processes such as cutting, wiring, packaging or the like. If a display for TV is directly made by using this method, in simple calculation, TV of 40 inches may be produced by connecting 5 to 40 wafers of 2 to 8 inches. Therefore, in order to directly implement a display of a TV level with LED elements by using a known manufacturing technique, there are numerous problems not overcome by the present techniques. In addition, in order to implement full-color, red-green-blue three-color LED elements should be put into a single pixel, and an LED full-color display may not be implemented by simply joining red-green-blue LED wafers.
In order to implement a high efficiency LED display, there may be used a bottom-up manner in which a III-V group film and a nanorod LED element are directly grown at patterned pixel sites of a large-sized glass substrate for an actual display. As known in many studies until now, in the MOCVD method where an III-V group film is grown, a process of directly depositing to a large-sized substrate such as a display for TV is not possible in view of equipment. Moreover, it is known in the art that growing a high crystallinity/high efficiency III-V group film and a nanorod heterojunction LED element on a transparent electrode patterned on a transparent amorphous glass substrate is very difficult in view of crystallography. Due to such technical limits, a method for implementing a full-color display for TV or monitor by directly growing LED elements on a large-sized glass substrate without using a small element is substantially not attempted.
Another approach prosecuted by many researchers to implement an LED display is a bottom-up manner based on the nano technology. In this method, a nanorod-type LED is grown on a single crystal substrate, and then this is partially picked and rearranged in a bottom-up manner on an electrode patterned with pixels, thereby implementing a large-sized display. However, a nanorod LED manufactured in the bottom-up manner has seriously bad light emission efficiency in comparison to a film-type LED grown on an existing wafer. Therefore, even though an LED display is implemented using this technique, the efficiency deterioration problem may not be easily solved for a considerable period. Moreover, in order to arrange nanorod LED elements grown in the bottom-up manner on an electrode by means of self-assembling of the bottom-up manner, it is essential to obtain nanorod elements having the uniform size and height. However, if a nanorod growth method such as vapor-liquid-solid (VLS) method well known in the art is used, the possibility of mass-production of nanorod LED elements having the uniform size and characteristics suitable for self-assembling is very low.
As another scheme, there is a top-down manner in which an LED display is implemented by cutting high efficiency LED elements. Generally, in this method, a display is implemented by arranging a single micro LED element prepared in the top-down manner at each sub-pixel site of a large-sized glass substrate in one-to-one relation. In detail, an LED display of a micrometer size has been developed for a small micro LED display, since individual micro LEDs prepared in the top-down manner are manufactured into each sub-pixel. In this case, after the LED element is grown on a sapphire substrate, the LED element is patterned into a micrometer size to make a micro LED element, and then an electrode is wired, thereby implementing a micro LED display smaller than the wafer substrate size. If this method is used, there is no problem in efficiency, but due to the limits in substrate size and manufacturing processes, it is impossible to implement an LED display of a large size.
As a result, a subminiature LED element manufactured using an existing top-down or bottom-up manner is highly likely to cause problems in efficiency and stability due to the increase of surface defects by an etching work. In addition, in case of an independent subminiature LED element, mutual cohesiveness is generated due to surface polarity among subminiature elements to form aggregates, which may result in many defects in a pixel patterning process. Therefore, manufacturing independent subminiature micro LED elements has a limit in implementing a high efficiency/large-sized LED display which allows mass production. Further, in the case a subminiature LED element prepared according to an existing method is located at a sub-pixel (pixel site) of an LED display substrate, due to the small size of the LED element, the subminiature LED element may not stand upright on the sub-pixel of the LED display but lie down or turn over.